Cutting small circles for masking

I ran into a problem trying to mask the wheels for my Airfix 1/72 Willies Jeep, my hand isn't steady enough to paint a perfect circle, and the rims aren't very pronounced. My circle cutter coulnd't cut anything close to what I needed. Recently I went into an art supply when I came across these small hobby blades from XACTO, they fit a handle used to cut stencils. I put one of these blades in a compass, used for drawing circles, and was able to cut out masks small enough for the wheels. Use multiple light passes rather than one heavy cut. Hope this helps, it helped me.

More often than not, I do the same thing as Blacksheep. I have a fairly thin mix of very dark grey that I use for tires. With the thin paint, I just have to get close to the rim and the paint will get pulled right on around.

If I do have to cut a mask, I use an Olfa circle cutter. Also had the problem of it not being able to cut a small diameter circle, so I heated up the plastic (the part that holds the needle) and bent it in towards the blade, to where it is almost touching.

What I do is to paint the "rim" color first, let it dry, then use what we call Prestick, or Blue tack that side of the pond to mask it. Small blob and I use a toothpick to shape it, then paint the rest in black for the tires.